The effect of surfactant monolayers on the heat transfer through air/water and oil/water interfaces using IR imaging technique

An experimental investigation on the effect of surfactant monolayers on the heat transfer through air/water and oil/water interfaces was carried out by observing the changes of surface temperature with LR Imaging Radiometer (Model 760). The heat transfer resistance of various single component and mixed monolayers at air/water and oil/water systems was studied. The results show that the surfactant monolayers introduce a noticeable heat transfer resistance to the heat transfer process across the interface. The solid monolayers exhibit lower resistance to heat transfer than the liquid monolayers at the oil/water interface. At air/water interface, the presence of monolayer decreases the evaporative cooling process and therefore increases the surface temperature rapidly. However, the presence of a monolayer at oil/water interface increases the heat transfer resistance across the oil/water interface. Heat transfer resistance increases as the chain length of fatty acid increases at the oil/water interface. The effects of phase-transition from a two-dimensional solid to the liquid state in cholesterol-arachidyl mixed monolayers was observed from the change in heat transfer resistance of the monolayers at the oil/water interface. The optimum molecular packing at the 1:3 molecular ratio in mixed surfactant monolayers of oleic acid-cholesterol and stearic acid-stearyl alcohol at the oil/water interface was also observed by this technique. (C) 1998 Academic Press.